Clock and mode signals for header and data communications

ABSTRACT

Data is communicated through two separate circuits or circuit groups, each having clock and mode inputs, by sequentially reversing the role of the clock and mode inputs. The data communication circuits have data inputs, data outputs, a clock input for timing or synchronizing the data input and/or output communication, and a mode input for controlling the data input and/or output communication. A clock/mode signal connects to the clock input of one circuit and to the mode input of the other circuit. A mode/clock signal connects to the mode input of the one circuit and to the clock input of the other circuit. The role of the mode and clock signals on the mode/clock and clock/mode signals, or their reversal, selects one or the other of the data communication circuits.

This application is a divisional of application Ser. No. 13/664,022,filed Oct. 30, 2012, now U.S. Pat. No. 8,634,508, issued Jan. 21, 2014;

Which was a divisional of application Ser. No. 13/312,051, filed Dec. 6,2011, now U.S. Pat. No. 8,325,866, granted Dec. 4, 2012;

Which was a divisional of application Ser. No. 12/946,439, filed Nov.15, 2010, now U.S. Pat. No. 8,094,765, granted Jan. 10, 2012;

Which was a divisional of application Ser. No. 12/760,016, filed Apr.14, 2010, now U.S. Pat. No. 7,852,974, granted Dec. 14, 2010;

Which was a divisional of application Ser. No. 12/465,990, filed May 14,2009, now U.S. Pat. No. 7,720,186, granted May 18, 2010;

which was a divisional of application Ser. No. 12/175,679, filed Jul.18, 2008; now U.S. Pat. No. 7,555,086, granted Jun. 30, 2009;

which was a divisional of application Ser. No. 11/857,697, filed Sep.19, 2007, now U.S. Pat. No. 7,415,087, granted Aug. 19, 2008;

which was a divisional of application Ser. No. 11/623,572, filed Jan.16, 2007, now U.S. Pat. No. 7,286,623, granted Oct. 23, 2007;

which was a divisional of application Ser. No. 11/198,064, filed Aug. 5,2005, now U.S. Pat. No. 7,180,971, granted Feb. 20, 2007;

which was a divisional of application Ser. No. 10/114,572, filed Apr. 2,2002, now U.S. Pat. No. 6,944,247, granted Sep. 13, 2005;

which was a divisional of application Ser. No. 09/443,186, filed Nov.19, 1999, now U.S. Pat. No. 6,393,081, granted May 21, 2002;

Which claimed priority from Provisional Application No. 60/109,880,filed Nov. 25, 1998.

BACKGROUND

1. Field

Circuits that communicate data may have data inputs for inputting data,data outputs for outputting data, a clock input for timing orsynchronizing the data input and/or output communication, and a modeinput for controlling the data input and/or output communication.

2. Description of the Related Art

In FIG. 1, a conventional circuit 110 has a data input bus 101, a dataoutput bus 102, clock input bus 103, and mode input bus 104. The circuit110 responds to the clock input and mode input to either, (1) remain inan idle state where no data communication occurs, or (2) enter a datacommunication state where data is communicated between the circuit'sdata input and/or data output.

While the circuit example in FIG. 1 is intentionally simple forclarification, its input/output signaling model, consisting of datainput, data output, clock input, and control input signals, couldrepresent more complex circuits. For example the circuit model couldrepresent IEEE 1149.1 test access port circuits implemented inintegrated circuits or included in the design layout or data base ofintellectual property core circuits, such as CPUs and DSPs, for use assub-circuits within an integrated circuit. Further, the example circuitmodel could represent, in general any type, of data communicationcircuits, such as shift registers, synchronously operated memories,micro-controllers, CPUs, DSPs, analog to digital converters whereby thedata input is understood to be analog signal data input, or digital toanalog converters whereby the data output is understood to be analogsignal data output.

In FIG. 2, the clock signals input on bus 103 time the circuit tooperate, in response to mode input on bus 104, in either an idle state202 or communicate state 204. The circuit 110 will be in the idle state202 during clocks signals occurring while the mode signal on bus 104 islow, and will transition to the communicate state 204 during a clocksignal occurring when the mode signal on bus 104 is high. The circuitwill remain in the communicate state 204 during clock signals occurringwhile the mode signal is high. The circuit will return to the idle state202 during a clock signal occurring when the mode signal is low.

In the idle state, no data communication occurs in the circuit from thedata input and/or data output. In the communicate state, datacommunication occurs in the circuit 110 from the data input and/or dataoutput. It should be understood that the state diagram of FIG. 2 isintentionally simplified to clarify the description of the invention. Amore complex state diagram, having at least an idle state and at least adata communication state could have been used as well. For example, thestate diagram of the above mentioned IEEE 1149.1 test access portcircuit contains an idle state (RTIDLE) and data communication states(DR-Shift & IR-Shift) and could have been used. However, for the purposeof describing the invention, the FIG. 2 state diagram is adequate.

In FIG. 3, circuit 110 operates according to the state diagram of FIG.2. In FIG. 3, the circuit 110 remains in the idle state during clocksignals occurring while the mode signal is low. The circuit 110transitions into the communicate state during the first clock signalthat occurs after the mode signal goes high. The circuit remains in thecommunicate state during clocks occurring while the mode signal is high.The circuit transitions back to the idle state during the first clockthat occurs after the mode signal goes back low.

The communicate state could operate a circuit as shown in FIG. 1 to: (1)transfer data inputs directly, through an enabled buffer or switch, todata outputs of the circuit; (2) transfer data inputs to the dataoutputs via intermediate storage circuitry within the circuit; (3) inputdata to the circuit, process the input data using processing circuitrywithin the circuit, and output the processed data; (4) input data to thecircuit and store the data in a internal memory; (5) output datapreviously stored in an internal memory; or (6) input and store datawhile outputting previously stored data.

In this specification, the mode input is evaluated on the rising edge ofthe clock input to determine state transitions. Also, the clock inputwill operate as a low to high and high to low pulse that occurs duringtimes when the mode input is in a steady state one or zero logiccondition. While a rising edge clock pulse convention is used in thisdescription, a falling edge clock pulse convention could be used aswell. Also the mode inputs may be inverted from what is shown in FIG. 3without departing from the nature of the present invention.

SUMMARY

The present invention provides a way to communicate data through twoseparate circuits or circuit groups, each having clock and mode inputs,by sharing and reversing the role of the clock and mode inputs.

A first advantage of the present invention is that it provides a methodof augmenting a second data communication protocol on a pair of controlsignals, clock and mode, originally designed to use only a first datacommunication protocol. A second advantage of the present invention isthat it provides a method of designing new circuits to utilize first andsecond data communication protocols on the same control signal wiring. Athird advantage of the present invention is that it reduces the wiringrequired for communicating data through separate circuits, since theclock and mode input wiring, as well as the data input and data outputwiring, may be shared between the separate circuits.

A fourth advantage of the present invention is that it provides a methodof accessing backup or redundant circuitry in a fault tolerant systemenvironment by reuse of the same control bussing for accessing eitherthe primary or backup circuitry. A fifth advantage of the presentinvention is that it provides a method of accessing shadow circuitry,i.e. special circuitry used by the manufacturer or end user for test,debug, diagnostics, emulation, or software development, by reuse of thesame control bussing for accessing either the functional or shadowcircuitry.

The circuits described herein could represent; (1) a printed circuitboard, (2) an integrated circuit, or (3) individual sub-circuits withinan integrated circuit.

DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of a known circuit.

FIG. 2 is a block state diagram of the known circuit.

FIG. 3 is a timing diagram of the known circuit.

FIG. 4 is a block diagram of a circuit arrangement according to thepresent invention.

FIG. 5 is a timing diagram for the operation of the circuit arrangementof FIG. 4.

FIG. 6 is a block diagram of a circuit arrangement according to thepresent invention;

FIG. 7 is a state diagram for the operation of the circuit arrangementof FIG. 6.

FIG. 8 is a timing diagram for the operation of the circuit arrangementof FIG. 6.

FIG. 9 is a block diagram of a circuit arrangement according to thepresent invention.

FIG. 10 is a block diagram of a selection circuit.

FIG. 11 is a state diagram for the operation of the selection circuit ofFIG. 6.

FIG. 12 is a block diagram of a circuit arrangement according to thepresent invention.

FIG. 13 is a block diagram of a circuit arrangement according to thepresent invention.

FIG. 14 is a block diagram of a circuit arrangement according to thepresent invention.

DETAILED DESCRIPTION

In FIG. 4, circuit arrangement 400 includes two circuits 401 and 402,similar to the example circuit 110 of FIG. 1, which are also labeled ascircuit 1 and circuit 2. A first shared connection 403 is formed betweencircuit 1's clock input, circuit 2's mode input, and a clock/modesignal. A second shared connection 404 is formed between circuit 1'smode input, circuit 2's clock input, and a mode/clock signal.

The naming convention given to the clock/mode signal on connection 403and the mode/clock signal on connection 404 is used to indicate thateach signal is shared for providing two input functions. During thefirst input function, the clock/mode and mode/clock signals form asignal pair used to operate circuit 1's clock and mode inputs,respectively, according to the example state and timing diagrams ofFIGS. 2 and 3 via shared connections 403 and 404. During the secondinput function, the clock/mode and mode/clock signals form a signal pairused to operate circuit 2's mode and clock inputs, respectively,according to the example state and timing diagrams of FIGS. 2 and 3 andvia shared connections 403 and 404.

The data input 101 connections and data output 102 connections ofcircuit 1 and circuit 2 may also be shared, as indicated by the dottedlines 405 and 406. Sharing data input and data output connectionsfurther reduces wiring area overhead. If the connections are shared, theoperating circuit will input and/or output data via the sharedconnections. The non-operating circuit will remain idle and will disableits data outputs to avoid contention with the data outputs from theoperating circuit.

If the data inputs and/or outputs of the circuits differ in that, forexample, circuit 1 inputs analog signal data and circuit 2 inputsdigital data, separate data inputs to the circuits will be maintained,as indicated by dotted line 407. Similarly, separate outputs will bemaintained as indicated by dotted line 408 if, for example, circuit 1outputs digital data and circuit 2 outputs analog signal data.

In FIG. 5, the shared clock/mode and mode/clock signals are operated ina role reversal manner to enable data communication to occur in eithercircuit 1 or circuit 2. Between times A and B, a first role of themode/clock and clock/mode signal pair causes circuit 1 to exit idle 1,enter communicate 1, and return to idle 1. Between times C and D, asecond role of the mode/clock and clock/mode signal pair causes circuit2 to exit idle 2, enter communicate 2, and return to idle 2. Betweentimes E and F, the first role of the mode/clock and clock/mode signalpair causes circuit 1 to exit idle 1, enter communicate 1, and return toidle 1.

The first role reversal of the mode/clock and clock/mode signal pairbetween operating circuit 1 and operating circuit 2 is seen to occurbetween times B and C. The second role reversal of the mode/clock andclock/mode signal pair between operating circuit 2 and operating circuit1 is seen to occur between times D and E. While the example of FIG. 5shows alternating between operating circuit 1 and operating circuit 2,that need not be the case. For example, circuit 1 may be operatedconsecutively without operating circuit 2, and circuit 2 may be operatedconsecutively without operating circuit 1.

During access of circuit 1, between points A and B, the clock/modesignal acts as a clock input and the mode/clock signal acts as a datainput. During access of circuit 2, between points C and D, theclock/mode signal acts as a data input and the mode/clock signal acts asa clock input. From this it is seen that both of the signals are beingused as both a clock input to one circuit and a data input to the othercircuit. The timing between the two signals needs to be designed suchthat when one circuit is being accessed, the other circuit remains idle.

For example, at the beginning of a circuit 1 access, i.e. transitionbetween idle 1 and communicate 1 states, the mode/clock signaltransitions from low to high while the clock/mode signal is low. The lowto high transition on mode/clock is received by circuit 2 as a clockinput transition, but since clock/mode is low during the low to hightransition of mode/clock, circuit 2 remains in the idle 2 state, asshown in the FIG. 2 state diagram. Thus, as circuit 1 is accessed,circuit 2 remains idle.

Similarly, at the beginning of a circuit 2 access, i.e. transitionbetween idle 2 and communicate 2 states, the clock/mode signal goes fromlow to high while the mode/clock signal is low. The low to hightransition on clock/mode is received by circuit 1 as a clock inputtransition, but since mode/clock is low during the low to hightransition of clock/mode, circuit 1 remains in the idle 1 state. Thus,as circuit 2 is accessed, circuit 1 remains idle

In general, this role reversal timing works on any type of circuit 1 andcircuit 2 arranged as shown in FIG. 4, as long as the following elementsare provided. Element 1, each circuit 1 and circuit 2 should includeclock and mode type inputs. Element 2, each circuit 1 and circuit 2should include at least one state that idles the circuit. Element 3,each circuit 1 and circuit 2 should include at least one state thatoperates the circuit. Element 4, a first connection should exist betweenthe clock input of circuit 1 and the mode input of circuit 2. Element 5,a second connection should exist between the mode input of circuit 1 andthe clock input of circuit 2. Element 6, signals driving the first andsecond connections should be timed such that when circuit 1 is in itsoperating state, circuit 2 remains in its idle state, and when circuit 2is in its operating state, circuit 1 remains in its idle state.

The example of FIG. 4 may represent a fault tolerant system designwhereby circuit 1 is a primary circuit and circuit 2 is a backup orredundant circuit to circuit 1. If circuit 1 were to malfunction,circuit 2 could be controlled to come on line to maintain the operationof the system. It is seen that control for operating the primary orbackup circuitry is achieved by the role reversal modes of theclock/mode and mode/clock signals, as described above. The circuitarrangement of FIG. 4 could represent one of many such primary andbackup circuit arrangements in a system comprising many integratedcircuits, or within a single integrated circuit.

The example of FIG. 4 may also represent a circuit arrangement wherebycircuit 1 is functional circuitry and circuit 2 is shadow circuitry forperforming test, debug, diagnostics, emulation, or software developmenttasks on the functional circuitry. During operation, circuit 1 andcircuit 2 would be separately enabled and disabled to bring about theabove mentioned shadow circuitry tasks. It is seen that control foroperating the functional or shadow circuitry is achieved by the rolereversal modes of the clock/mode and mode/clock signals, as describedabove. The circuit arrangement of FIG. 4 could represent one of manysuch functional and shadow circuit arrangements in a system comprisingmany integrated circuits, or within a single integrated circuit.

In the timing diagram of FIG. 5, when circuit 1 enters the idle 1 statefrom the communicate 1 state, at time B, circuit 2 is already in theidle 2 state at that time. If desired, the clock/mode signal could gohigh prior to mode/clock pulse at C to cause circuit 2 to immediatelyenter the communicate 2 state instead of remaining in the idle 2 stateduring the clock pulse at time C. This is true also for the clocking attimes D and E, where circuit 1 may immediately enter the communicate 1state instead of remaining in the idle 1 state during the clock pulse attime E.

In FIGS. 4 and 5, identical circuits may be controlled using rolereversal of the clock/mode and mode/clock signals. In FIGS. 6, 7, and 8,non-identical circuits can also be controlled using the role reversal ofclock/mode and mode/clock signals.

In FIG. 6, circuit 1 601 is assumed to be the same as circuit 1 in FIG.4 and to operate according to the state diagram of FIG. 2. However,circuit 2 610 of FIG. 6 is different to the extent that it operatesaccording to the state diagram of FIG. 7. Both circuits 601 and 610operate in response to a clock and mode input pair and both circuits areconnected at their clock, mode, data input, and data output aspreviously described in regard to FIG. 4.

In FIG. 7, the state diagram of circuit 2 610 includes an idle state,header 1 state, header 2 state, communicate state, trailer 1 state, anda trailer 2 state. The header 1 and 2 states form an entry protocol intothe communicate state, and trailer 1 and 2 states form as exit protocolfrom the communicate state. The communicate state can only be entered ifa correct entry protocol has been received. Likewise, the communicatestate can only be exited if a correct exit protocol has been received.While this process provides a higher degree of fault tolerance inentering and exiting the communicate state, it is primarily provided toillustrate how the present invention can be used on circuits whichoperate in response to different control input protocols.

In FIG. 8, circuit 1 601 and circuit 2 610 are accessed using the rolereversing mode/clock and clock/mode inputs. The FIG. 8 timing diagram isvery similar to the FIG. 5 timing diagram in that it shows circuit 1being accessed between points A and B while circuit 2 is idle, andcircuit 2 being accessed between points C and D while circuit 1 is idle.What is important to see in the circuit and timing examples given inFIGS. 4, 5, 6, and 8, is that the role reversing control input schemeworks with circuits having the same or different control inputprotocols.

In FIG. 9, circuit arrangement 900 comprises a selection circuit 910,circuit 1 901, circuit 2 902, And gate 940, and And gate 950. Circuit 1and circuit 2 are circuits to be accessed. Selection circuit 910 is usedto select which circuit, i.e. circuit 1 or circuit 2, will be accessed.A data input bus 101 is connected to the data inputs of selectioncircuit 910, circuit 1, and circuit 2. A data output bus 102 isconnected to the data outputs of selection circuit 910, circuit 1, andcircuit 2.

The clock/mode signal bus 403 is connected to the clock input ofselection circuit 910, one input of And gate 940, and to one input ofAnd gate 950. The mode/clock signal bus 404 is connected to the modeinput of selection circuit 910, the clock input of circuit 1, and theclock input of circuit 2. The other input of And gate 940 is connectedto an enable circuit 1 (EC1) signal output from selection circuit 910.The other input of And gate 950 is connected to an enable circuit 2(EC2) signal output from selection circuit 910. The output of And gate940 is connected to the mode input of circuit 1, and the output of Andgate 950 is connected to the mode input of circuit 2.

Circuits 1 901 and circuit 2 902 operate according to the state diagramspreviously described in regard to FIGS. 2 and 7.

The circuit arrangement 900 operates, using the role reversal techniquedescribed previously in regard to FIGS. 4 and 6, to communicate datathrough either selection circuit 910, or through one of the two circuits1 and 2. Data communication through selection circuit 910 is used toselect which circuit, 1 or 2, will communicate data when the role of theclock/mode and mode/clock signals are reversed from accessing theselection circuit 910 to accessing the selected circuit 1 or 2.

Following data communication to selection circuit 910, either the EC1signal will be set high and EC2 signal will be set low to allow accessof circuit 1 via And gate 940, or the EC2 signal will be set high andthe EC1 signal will be set low to allow access of circuit 2 via And gate950. When EC1 is high, and a role reversal of the clock/mode andmode/clock signals occurs, from accessing select circuit 910 toaccessing circuit 1 or 2, the clock/mode signal will pass through Andgate 940 to the mode input of circuit 1, to enable its access.Similarly, when EC2 is high, and a role reversal of the clock/mode andmode/clock signals occurs, from accessing select circuit 910 toaccessing circuit 1 or 2, the clock/mode signal will pass through Andgate 950 to the mode input of circuit 2, to enable its access.

When circuit 1 is being accessed, circuit 2 will be forced to remainidle by the low EC2 input to And gate 950. Likewise, when circuit 2 isbeing accessed, circuit 1 will be forced to remain idle by the low EC 1input to And gate 940. The data outputs of select circuit 910, circuit1, and circuit 2 are disabled when the circuits are idle and are enabledwhen they are accessed. Thus only the accessed circuit drives the dataoutput buss 102.

From the above it is seen that during a first role of the clock/mode andmode/clock signals, communication with the selection circuit 910 occurs,and during a second role of the clock/mode and mode/clock signals,communication to either circuit 1 or circuit 2 occurs, depending on thesettings of EC1 and EC2. The selection circuit 910 serves to amplify thenumber of circuits that can be accessed using the role reversing controlinput technique. While two circuits, i.e. circuit 1 and 2, are shown tobe selectively enabled to operate in response to a role reversal ofclock/mode and mode/clock, any number of circuits could be selectivelyenabled to operate as well.

For example, selectively accessing one of twenty circuits, like circuits1 and 2, would simply require twenty EC signal outputs (EC1-EC20) fromthe selection circuit 910, each EC signal enabling or disabling accessto each of the twenty circuits via an And gate as shown in arrangement900.

Further, the arrangement 900 could be altered to where a group ofserially connected circuits, such as a group of serially connectedcircuit is, could be selected by a single EC signal and accessed at thesame time. A group of serially connected circuit is would be connectedsuch that the data output of a leading circuit 1 feeds the data input oftrailing circuit 1. Also, the first circuit 1 of the group would inputfrom the data input bus 101 while the last circuit 1 of the group wouldoutput onto the data output bus 102. Such a group of serially connectedcircuit is would have a common first connection at their clock inputsand a common second connection at their mode inputs. It should be clearthat other circuit 1 and/or circuit 2 selection and access arrangementsare possible as well.

In FIG. 10, the selection circuit 910 comprises a 1-bit shift register1010, a 1-bit update register 1015, a 2-bit finite state machine (FSM)1020, a 3-state buffer 1030, and an inverter 1040. The shift register1010 has a serial data input from data input bus 101, a serial dataoutput 1002 connected to the input of 3-state buffer 1030, control inputfrom control bus 1050 from the 2-bit finite state machine 1020, and aselection output bus 1060.

The 1-bit update register 1015 is connected to the output bus 1060 andto the control input bus 1050. The update register 1015 outputs the EC2signal on bus 1070 to the input of inverter 1040 and to the captureinput of the shift register 1010. Inverter 1040 outputs the EC1 signal.The state machine 1020 has a clock input from clock/mode bus 403 and amode input from mode/clock bus 404. The state machine 1020 outputscontrol to the shift register 1010, update register 1015, and 3-statebuffer 1030. When enabled, the 3-state buffer 1030 outputs data ontodata output bus 102. Circuits 1 and 2 of arrangement 900 are assumed toalso contain 3-state output buffers that can be enabled to output dataonto data output bus 102 when they are accessed.

In FIG. 11, the 2-bit finite state machine 1020 provides an idle state,a capture state, a shift data state, and an update state. In the idlestate, the state machine outputs control to disable the 3-state buffer1030. In the capture state, the state machine enables shift register1010 to capture the data output from the update register 1015 via bus1070. In the shift state, the state machine enables 3-state buffer 1030and controls the shift register 1010 to shift data from the data inputbus 101, through the shift register bit, and to the data output bus 102.In the update state, the state machine outputs control to updateregister 1015 to load data from the shift register via bus 1060.

The state machine returns to the idle state following the update state.The data loaded into the update register is output from selectioncircuit 910 on the EC1 and EC2 outputs. If a logic zero was shifted inand updated, EC1 is high to enable circuit 1 of arrangement 900 and EC2is low to disable circuit 2 of arrangement 900. If a logic one wasshifted in and updated, EC 1 is low to disable circuit 1 and EC2 is highto enable circuit 2. The update register 1015 prevents data transitionson the EC 1 and EC2 outputs as data shifts through the shift register1010 during the shift state.

In FIG. 10, if more than two circuits need to be selected in arrangement900, the bit length of the shift and update registers would increase toallow for a larger number of EC outputs, and the decode logic at theoutput of the update register would increase beyond the inverter 1040.For example, a four bit shift and update register and expanded decodelogic combination could select any one of up to sixteen circuits. Whilethe length of the shift register 1010 and update register 1015 grow toaccommodate a greater circuit selection capability, the size of the2-bit state machine 1020 remains the same.

In regard to FIG. 9 and FIG. 10, the serial data input bus 101 to andserial data output bus 102 from the selection circuit 910 is only onebit wide. However, the data input bus 101 to and data output bus 102from circuits 1 and 2 of arrangement 900 may be either a serial orparallel bus. Thus the data input and output width of the selectioncircuit 910 may differ from the data input and output width of thecircuits 1 and 2 in arrangement 900. Also, the data input and/or outputwidths of the circuits 1 and 2 themselves may differ. For example,circuit 1 may have a 32-bit wide data input and output bus, whilecircuit 2 may have a 16-bit wide data input and output bus. Thepotential for circuits to have varying data input and data output buswidths applies to all circuit examples shown in this specification.

In FIG. 12, arrangement 1200 is very similar to arrangement 900 andillustrates that a plurality of IEEE 1149.1 standard test access port(TAP) circuits 1220 may be selected for access using the role reversingcontrol input technique in combination with the selection circuit 910. ATAP circuit is a very well understood and highly used circuit. The TAPis designed into almost every major microprocessor, micro-controller,and digital signal processor integrated circuit, as well as ASICs. It isalso included in the design layout or data base of many intellectualproperty core circuits, such as microprocessors, micro-controllers, anddigital signal processors, which are used to design highly complexsystem-on-chip integrated circuits. The ability to selectively access aTAP or a selected group of TAPs to bring about testing, emulation,and/or debug is very advantageous, especially in system-on-chipintegrated circuits comprising multiple intellectual property corecircuits, each including a TAP.

The differences between the arrangements 1200 and 900 include; (1) atest data input (TDI) signal is connected to input serial data on datainput bus 101, (2) a test data output (TDO) signal is connected tooutput serial data on data output bus 102, (3) a role reversing testclock/test mode select (TCK/TMS) signal is connected to input on controlbus 403, (4) a role reversing test mode select/test clock (TMS/TCK)signal is connected to input on control bus 404, (5) a TAP 1 1220 issubstituted for circuit 1 901, and (6) a TAP 2 1220 is substituted forcircuit 2 902.

The IEEE 1149.1 standard defines the TAP circuit 1220 and the way theTAP operates in response to its local TMS 1240, TCK 1242, TDI 1241, andTDO 1243 signals. To the invention, the TAP 1 and TAP 2 are viewed asjust another type of circuit that can be selected and accessed aspreviously described in regard to FIGS. 9, 10, and 11. For example, theTAP's local TMS input 1240 is viewed as the local mode input of circuit1 or 2, the local TCK input 1242 is viewed as the local clock input ofcircuit 1 or 2, the local TDI input 1241 is viewed as the local input ofcircuit 1 or 2, and the local TDO output is viewed as the local outputof circuit 1 or 2.

The simplicity of using the role reversing control input technique toeither access the selection circuit 910 to select a TAP, or to accessthe TAP selected is an important aspect of the present invention.Implementers of this invention will appreciate this simplicity. The lowoverhead of using the role reversing control input technique incombination with the selection circuit 910 will also be appreciated,since the silicon overhead for the selection circuit 910 is very small,and no additional busing wires, beyond the TDI bus 101, TDO bus 102,TCK/TMS bus 403, and TMS/TCK bus 404, are required to interface a TAPcontroller up to any number of TAPs 1220.

In FIG. 13, a fully programmable TAP selection and access arrangement1300 uses the role reversing control input technique in combination witha selection circuit 910 and programmable TAP connection circuitry 1310.The programmable TAP connection circuitry 1310 is connected to: (1) theTDI bus 101, (2) the TDO bus 102, (3) the TCK/TMS bus 403, (4) theTMS/TCK bus 404, (5) the selection circuit via control bus 1320, and (6)to the local TMS, TCK, TDI, and TDO signals of each TAP 1-N 1220.

The control output on bus 1320 from the selection circuit comes from theupdate register 1015 which is loaded following a shift operation throughthe shift register 1010 as previously described in regard to selectioncircuit 910. The control can be either decoded locally within theselection circuit 910, as previously described, or it can be outputdirectly from the update register 1015 and decoded within theprogrammable TAP connection circuitry 1310.

In response to control output from the selection circuit 910, theprogrammable TAP connection circuitry 1310 can connect any TAP to TDIbus 101, TDO bus 102, TCK/TMS bus 403, and TMS/TCK bus 404 as previouslydescribed in FIGS. 9 and 12. Further, the programmable TAP connectioncircuitry contains additional switching circuitry responsive to thecontrol output from selection circuit 910 to serially link any of theTAPs 1220 together in a group and connect the serially linked TAP groupto the TDI bus 101, TDO bus 102, TCK/TMS bus 403, and TMS/TCK bus 404,such that the entire TAP group may be simultaneously accessed.

The operation of the circuit arrangement 1300 is very similar to thatdescribed in FIGS. 9, 10, 11, and 12 above, in that: (1) during a firstrole of the TCK/TMS and TMS/TCK inputs the selection circuit 910 isaccessed to select a TAP or a serially linked TAP group, and (2) in asecond role of the TCK/TMS and TMS/TCK inputs the selected TAP orserially linked TAP group is accessed from TDI bus 101 to TDO bus 102.The difference between the circuit arrangements of FIG. 13 and FIGS. 9and 12 is the ability of the programmable TAP connection circuitry 1310to select any desired ones of the TAPs 1-N 1220, in any order orarrangement, so that the selected TAP group can be simultaneouslyaccessed via TDI bus 101 and TDO bus 102. As with FIGS. 9 and 12,non-selected TAPs remain idle while selected TAPs are accessed.

While TAPs 1220 were shown in FIG. 13 as the circuits being selectedinto groups by the programmable TAP connection circuitry 1310, it shouldbe understood that any circuits, such as circuits 1 or 2 of FIG. 9,could be similarly selected into groups and accessed.

In FIG. 14 circuit arrangement 1400 illustrates an example of two chainsof serially connected TAPs 1220 being individually accessed using onlythe role reversing control input technique. The first chain, comprisingTAPs 1 through N, is accessed from TDI bus 101 to TDO bus 102 using afirst role of the TCK/TMS and TMS/TCK control inputs on buses 403 and404, respectively. The second chain, comprising TAPs 1 through M, isaccessed from TDI bus 101 to TDO bus 102 using a second role of theTCK/TMS and TMS/TCK control inputs on buses 403 and 404, respectively.

When the first chain of TAPs is accessed, the second chain of TAPsremain idle. When the second chain of TAPs is accessed, the first chainof TAPs remain idle. The two chains may contain other types of circuits1-N and 1-M, instead of TAP circuits. Also, the data input and outputwidth of chains containing other circuit types may differ, as previouslymentioned.

In FIGS. 4, 6, 9, 12, 13, and 14, input busses 101, 403, 404, and outputbus 102 could be connected to: (1) terminals on an intellectual propertycore containing circuits 110, 401, 402, 601, 610, 910, or 1220, (2) padson an integrated circuit containing circuits 110, 401, 402, 601, 610,910, or 1220, or (3) connectors on a printed circuit board containingcircuits 110, 401, 402, 601, 610, 910, or 1220. A communicationcontroller connected to these core terminals, integrated circuit pads,or printed circuit board connectors could be used to control thecommunication to the circuits 110, 401, 402, 601, 610, 910, or 1220using the role reversing control input method described above.

What is claimed is:
 1. A process of communicating with a communicationdevice comprising: A. receiving over a clock signal lead and a modesignal lead a communication device steady state signal and alternatingsignals indicating a message header; B. receiving over the clock signallead and the mode signal lead a steady state signal and alternatingsignals indicating communication of a message; and C. receiving over oneof the clock signal lead and the mode signal lead alternating signalsused to receive data signals of the message on a serial data input leadof the communication device.
 2. The process of claim 1 in which thecommunication device: i. receives a clock signal of one state whilereceiving a mode signal of alternating states; and ii. then receives aclock signal of another state while receiving a mode signal ofalternating states to indicate a message header.
 3. The process of claim1 in which the communication device: i. receives a clock signal of onestate while receiving a mode signal of alternating states; ii. thenreceives a clock signal of another state while receiving a mode signalof alternating states to indicate a message header; and iii. thenreceives a clock signal of the one state while receiving mode signals ofalternating states to receive the data signals of the message.
 4. Theprocess of claim 1 including stepping state machine circuitry of thecommunication device through states of idle, header, and communicate inresponse to the clock signals and mode signals.